Several hundred suicide bombers and 4,000 fighters belonging to Isis are preparing to defend Hajin in eastern Syria close to the border with Iraq.

The town is the last stronghold of the Islamic State, the militarised Islamic cult that three years ago controlled territory the size of Great Britain.

The struggle for Hajin comes exactly a year after Isis suffered a decisive defeat with the capture of Mosul on 10 July 2017 by Iraqi forces backed by a US-led coalition.

Multiple anti-Isis forces are now closing in on Hajin, which is on the east bank of the Euphrates in Deir ez-Zor province, says a local eyewitness who spoke to The Independent after escaping to Kurdish-held territory.

“I heard from people who are working with Daesh [Isis] officials that there are more than 200 child suicide bombers, called the Lion Cubs, in Hajin,” said Sattam, 32, an Arabic teacher who lived until recently in Bahara, a northern neighbourhood of Hajin.

“There are still more than 35,000 people and 4,000 Daesh in the town,” he said, adding that his relatives, who are still in Hajin, say that Isis has dug deep tunnels there to protect themselves from aerial attack.

He believes that the struggle for Hajin might take longer than the four-month siege of Raqqa, the de facto Isis capital in Syria which was captured by the US-supported Syrian Democratic Forces, a Kurdish-Arab group, in October.

Sattam says that Hajin is being regularly shelled and hit by airstrikes, but it has yet to be seriously attacked by ground forces.

The Iraqi government says that its F-16 bombers targeted a meeting of Isis leaders in three houses, linked by a tunnel, in Hajin on 23 June and killed 45 of them.

The dead included the Isis deputy war minister, chief of police and a messenger of Abu Bakr al-Baghdadi, the self-declared caliph of the Islamic State, who is thought to currently be in the Syria-Iraq border area.

Sattam, who does not want to give his full name because he has a cousin, a farmer, still living in Hajin, gives a detailed picture of life in the last town held by Isis.

On a small scale, it maintains the complex administrative system with which it used to rule large cities like Mosul, Raqqa, Fallujah and Ramadi, as well as many towns in Syria and Iraq.

“I was in contact with some Iraqi friends who were working in the tax office of Daesh in Hajin,” says Sattam.

“They were collecting fees from people of the town who are rich because many are landlords and others have businesses in Saudi Arabia and Qatar.”

He says the town is well known locally for its large and well-decorated houses owned by traders who belong to powerful local tribes.

He says there was friction last summer between Isis and the people of Hajin: “I remember when some Iraqi and Syrian young men managed to set fire to a centre for Daesh security men.”

Whatever the timing of the final assault on Hajin, it will inevitably fall because it is encircled by three different armies.

Sattam ticks off the town’s besiegers: the coalition-backed SDF, a Kurdish-Arab force with Kurdish leadership to the north, northeast and west; the Iraqi Shia paramilitary Hashd al-Shaabi to the east; and the Syrian army of President Bashar al-Assad to the south.

One reason for the defeat of Isis, despite its military skills and fanaticism, is the sheer number of its enemies.

Asked about what was known locally of the whereabouts of al-Baghdadi, Sattam says that Isis members or those working for their institutions “no longer talk about him or any new statement or decision he made.”

He adds that the word is common in the Deir ez-Zor countryside that “even if the caliph is dead, he left hundreds of his sons as suicide bombers”.

This is not proof that al-Baghdadi is dead since, if this were true, it would either be admitted or be a secret closely held by his inner circle.

His 18-year-old son, Huthaifa al-Badri, was reported last week by Isis to have been killed fighting Russians and the Syrian army in Homs province in Syria. His martyrdom is being heavily promoted by Isis social media channels, though these are much diminished in volume and influence.

The SDF and the US-led coalition launched Operation Roundup on 1 May with the purpose of taking the last Isis-held territory along the Syria-Iraq border.

The offensive has already seized the only other town that was still held by Isis – Dashisha in Hasakah province – in June. Isis had occupied it for five years, during which conditions had become progressively grimmer for its inhabitants.

Salim Abu Ali, 48, a farmer from Dashisha, gave a graphic account to The Independent of life under Isis, in the town where he remained until it was captured by the SDF.

“I couldn’t leave the town because my wife is disabled and my sons left the country for Iraq in 2013 because Daesh had taken the town,” Salim says.

When Isis first took over in July 2013 they treated people well, he says, but the following year, probably because their victories had made them overconfident, they became more intimidating and started public executions.

“The horrible thing that I witnessed many times was that people did not realise that Daesh was going to behead them,” Salim says.

“I still remember a man I knew, Abu Mohammed, who was blindfolded and crying out that he was innocent, but suddenly a big knife cut into his neck, ripped through his throat, and suddenly blood gushed out.”

The man who had beheaded him was shouting: “God orders us to kill disbelievers without mercy.” Salim says that his friend had been accused by somebody who hated him of trading with the Syrian government.

He recalls that this happened in November 2016 when Isis fighters were angry because they were getting bad news from Mosul, which was being besieged by the Iraqi army.

Isis fighters began arriving from Iraq in large numbers with armoured vehicles and women prisoners. “Later we have been told they were Yazidis to be taken to Raqqa.”

The attack on Dashisha by the SDF began two months ago, accompanied by airstrikes every day.

“There wasn’t fighting in the town,” says Salim, “it was in the farms around Dashisha. Most of those who fought were foreigners, mostly from Azerbaijan.”

The local Isis fighters withdrew and many surrendered to the authorities in Syria or Iraq. Salim ended up being detained in a camp called al-Hol, run by the SDF, until he was rescued by a cousin who guaranteed that he was not a threat.

After a series of calamitous defeats in Iraq and Syria, Isis fighters may be getting demoralised and no longer as determined as before to fight to the end. If so, this would be good news for the thousands of people trapped in Hajin, waiting for the final battle to begin.